“Frac packing” is a combination of gravel packing and fracturing operations in unconsolidated subterranean formations in a hydrocarbon recovery endeavor. Modern frac packing operations utilize high-strength proppants in place of ordinary sand, which is typically used in gravel packing. The high crush resistance of the proppant, which is typically manufactured from either ceramic or bauxite material, allows fractures in the formation created during the hydraulic fracturing operation to remain open after pressure is released and the proppant is packed in the fracture tunnels. Ordinary sand used in this application would simply be crushed, due to the overburden pressure (closure stress) in the formation, allowing the fractures to close again and severely limit fluid inflow potential (i.e. the production of hydrocarbons). Without wishing to be limited to any particular theory, it appears that the harder the proppant used, the greater the problem with sticking. Of course, these same kinds of proppants are used in gravel packing operations that do not involve fracturing.
The use of these high-strength proppant materials can create a potentially severe problem for the downhole tool operation. Proppant wedged between the outer packer assembly and the internal service tool string (which is used to place the proppant) can cause the service tool to become stuck within the packer (and/or the seal bores). The available pulling limitation of the drill pipe workstring will not allow the proppant to be crushed or allow further movement of the service tool after initial sticking. This situation potentially leads to a very costly fishing operation, and delays the well being put on production.
The Baker Hughes CK FRAQ tool system illustrated in FIGS. 1A-1E incorporates an intermediary reverse circulation position (FIG. 1D) that is intended to allow the proppant in the tool system, after the fracturing operation is complete, to be circulated out prior to attempting to pull the service tool out of the packer. Unfortunately, this method is only partially successful in removing all of the proppant due to the propensity of the proppant to “stick” or adhere to the service tool. Without wishing to be limited to any particular theory, the “sticking” characteristic of the proppant is thought to be due to either a static electrical charge between the proppant and the steel of the service tool, cohesive forces of the carrier fluid, adhesive forces between the carrier fluid and the alloy or steel of the service tool or a combination of all. The attractive force between the proppant and/or the carrier fluid and steel results in failure to remove all of the excess proppant, which in some cases leads to sticking of the tool system.
It would be desirable if methods and/or compositions could be devised that would reduce or eliminate the sticking or wedging of proppant, in particular high strength proppant, to the tool system, the packer assembly or both to reduce the sticking of the tool system in the packer.